An MCL injury typically occurs after impact to the outside of the knee when the knee is in a slightly bent position. When impact occurs, the MCL on the inside of the knee stretches, and if the force is great enough, some or all of the fibers in the ligament will tear. People who participate in contact sports often experience these injuries, which are frequently accompanied by damage to other parts of the knee, including the menisci, ACL, or PCL. Young athletes may experience a fracture or other bone damage along with an MCL injury.
When an MCL injury occurs, individuals often experience immediate pain along with a “snap” or “pop” that may be felt or heard. Swelling may occur as well. MCL injuries are graded 1, 2, or 3, depending on the degree of damage. A grade 1 tear affects less than 10 percent of the fibers while a grade 3 represents a total rupture, and a grade 2 can fall anywhere in between. A grade 1 MCL injury involves mild tenderness, no swelling, and minor pain but no joint looseness. A grade 2 injury involves significant tenderness, some swelling over the ligament, some pain, and mild to moderate joint looseness. The pain associated with a grade 3 MCL injury can vary and there is significant joint looseness with possibly a very unstable knee.
An MCL injury should be taken seriously, as it can impact balance and the stability of the knee joint.